In many settings, it is helpful to be able to measure and monitor physiological data on a long-term, outpatient basis. Existing wireless devices have sensors that measure one or more of electrodermal activity (EDA), which is also known as galvanic skin response, heart rate (HR), heart rate variability (HRV), temperature and motion. One type of sensor used to measure HR and HRV is a photoplethysmograph (PPG).
However, existing wireless biosensor devices have a number of disadvantages. They are generally bulky, uncomfortable and poorly suited for long-term use on an outpatient basis. Nor are they well suited for long-term wear by infants or uncooperative patients, such as a patient with dementia who would tend to remove existing sensors. In addition, they are not well suited for ambulatory, long-term wear by animals.
Typically, existing EDA sensors have cumbersome electrodes. The measurement of skin conductance commonly requires clipping electrodes on the fingertips or using adhesive patches. This severely limits the user's ability to perform tasks requiring the hands. Also, long-term (e.g., weeks) of continuous wear using rubberized electrodes is uncomfortable, as is long-term use of standard metal medical electrodes and the adhesive pads used to apply them. Both of these tend to cause skin irritation when the skin does not breathe for many days of use.
In addition, existing devices are generally encased in relatively large plastic shell cases and are not comfortable or suitable for wearing for more than a few hours. Nor do they allow the wearer the freedom of movement typical of daily activity.
Moreover, existing systems with wireless connectivity generally exhibit a short battery life, and are not suitable for continuous wireless transmission for more than 12 hours. In chronic conditions (e.g. autism, sleep disorders, epilepsy, PTSD, bipolar disorder, etc.), there is a need to collect physiological data continuously over weeks and months. Given a typical coin cell battery with a capacity of a few hundred milli-amp hours, this requires that the average power consumption of the wearable system be 1 milliwatt or less. This level of power consumption cannot be achieved by radio design alone; it also requires proper design of the sensing hardware.
Also, existing wireless biosensor devices are generally limited to a single user and do not support data collection from multiple users simultaneously. In addition, another important concern with existing devices is their generally limited data analysis, e.g., simply to record data such as heart rate.